High-altitude platforms for wireless communications

The demand for high-capacity wireless services is bringing increasing chall enges, especially for delivery of the 'last mile'. Terrestrially, the need for line-of-sight propagation paths represents a constraint unless very lar ge numbers of base-station masts are deployed, while satellite systems have capacity limitations. An emerging solution is offered by high-altitude pla tforms (HAPs) operating in the stratosphere at altitudes of up to 22 km to provide communication facilities that can exploit the best features of both terrestrial and satellite schemes. This paper outlines the application and features of HAPs, and some specific development programmes. Particular con sideration is given to the use of HAPs for delivery of future broadband wir eless communications.